Variable Neutral Density (VND) Filter - STC Optics
Amazon.com : 67mm Variable Neutral Density NDX Filter for Sony Alpha A6000 : Electronics
Amazon.com : NiSi 77mm Swift True Color ND-Vario | 1-5 Stops Variable Neutral Density Filter | Adjustable ND, True-to-Life Color, No Vignetting, Optical Glass with Nano Coating | Photography and Videography : Electronics
Kase Wolverine 77mm Variable Neutral Density Filter 1104090301